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  Display device and manufacturing method thereofUSPTO Application #: 20080105877Title: Display device and manufacturing method thereof Abstract: A display device with improved reliability and a manufacturing method of the same with improved yield. A display device according to the invention comprises a display area including a first electrode, an insulating layer covering an edge of the first electrode, a layer containing an organic compound, which is formed on the first electrode, and a second electrode. The first electrode and the insulating layer are doped with an impurity element of one conductivity. (end of abstract) Agent: Eric Robinson - Potomac Falls, VA, US Inventors: Shunpei Yamazaki, Osamu Nakamura, Aki Yamamiti, Naoto Yamade USPTO Applicaton #: 20080105877 - Class: 257072000 (USPTO) Related Patent Categories: Active Solid-state Devices (e.g., Transistors, Solid-state Diodes), Non-single Crystal, Or Recrystallized, Semiconductor Material Forms Part Of Active Junction (including Field-induced Active Junction), Field Effect Device In Non-single Crystal, Or Recrystallized, Semiconductor Material, In Array Having Structure For Use As Imager Or Display, Or With Transparent Electrode The Patent Description & Claims data below is from USPTO Patent Application 20080105877. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a display device that comprises an element including a light emitting material sandwiched between electrodes (hereinafter referred to as a light emitting element), and to a manufacturing method of the display device. In particular, the invention relates to a display device using a light emitting material that generates EL (Electro Luminescence) (hereinafter referred to as an EL material). [0003] 2. Description of the Related Art [0004] In recent years, an EL display device utilizing electro luminescence (hereinafter referred to as EL) has been developed. The EL display device, as well as a liquid crystal display device that has been in practical use, comprises pixels arranged in matrix to display images. Known as a driving method of pixels are a passive matrix method and an active matrix method using transistors. In either case, what attracts attention is that self-luminous type pixels each including an EL element formed of an EL material provide wide viewing angle and high contrast. [0005] It is said that an EL element emits light through the following mechanism: a voltage is applied between a pair of electrodes that sandwich an organic compound layer, electrons injected from the cathode and holes injected from the anode are re-combined at the luminescent center of the organic compound layer to form molecular excitons, and the molecular excitons return to a ground state while releasing energy to cause the EL element to emit light. Excitation state includes a singlet exciton and a triplet exciton, and it is considered that luminescence can be made through either excitation state. [0006] However, an EL material (particularly, an organic EL material) that mainly constitutes an EL element is characterized in that it is sensitive to moisture and degrades easily. Therefore, a sealing technology is an essential part of manufacturing of an EL display device. Known as a sealing structure is the one in which a sealing member is provided so as to surround a display area including EL elements and a sealing substrate is formed with the sealing member interposed therebetween (for example, see Patent Document 1). [Patent Document 1] Japanese Patent Laid-Open No. 2003-255845 SUMMARY OF THE INVENTION [0007] Although the sealing structure allows a display area including EL elements to be sealed and prevents moisture from entering externally, it is not possible to inhibit completely degradation of an EL display device. That is, there may occur a punctuate non-light emitting area (including an area in which luminance is lowered partially) in pixels, a defect due to enlargement of the area (hereinafter referred to as a dark spot), and a defect in which a non-light emitting area at the periphery of pixels is enlarged with time (hereinafter referred to as a shrink). [0008] In view of the foregoing problems, the invention provides a display device that can prevent degradation of an EL material and a manufacturing method of the display device. [0009] According to the invention, an interlayer insulating film provided for planarization is required to have high heat resistance, high insulation properties, and a high planarization rate. Therefore, a heat resistant planarized film is preferably used. Such an interlayer insulating film is preferably formed by an application method typified by a spin coating method instead of a CVD method or a vapor deposition method. [0010] Specifically, it is desirable to use a heat resistant planarized film formed by an application method as an interlayer insulating film and an insulating layer (bank). The interlayer insulating film and the insulating layer (bank) are formed of an application film using a material that has a backbone structure obtained by binding silicon (Si) to oxygen (O) and has one or more substituents selected from hydrogen, fluorine, an alkyl group, and aromatic hydrocarbon. A film after being baked corresponds to a silicon oxide film (SiOx) containing an alkyl group. The silicon oxide film (SiOx) containing an alkyl group has a higher light transmittance than acryl resin and can endure heat treatment at a temperature of 300.degree. C. or more. [0011] According to the invention, an interlayer insulating film and an insulating layer (bank) are formed by an application method through the following steps. First, in order to increase the wettability, thinner pre-wet application is carried out after washing a substrate with purified water, and a liquid material called a varnish in which a low molecular weight component (precursor) with binding of silicon (Si) to oxygen (O) is dissolved in a solvent is applied on the substrate by a spin coating method or the like. Then, the varnish as well as the substrate is heated to accelerate volatilization (evaporation) of the solvent and crosslinking of the low molecular weight component, whereby a thin film can be obtained. Subsequently, an application film in a peripheral edge portion of the substrate is removed. In the case of an insulating layer (bank) being formed, the film may be patterned to obtain a desired shape. The film thickness is controlled by the spin rotation rate, the rotation time, the concentration and the viscosity of the varnish. [0012] The use of the same material for an interlayer insulating film and an insulating layer (bank) will result in the reduction of the manufacturing cost. Further, since devices such as the one for coating and for etching can be used in common, cost reduction can also be achieved. [0013] In general, ITO (Indium Tin Oxide) is employed for a first electrode (anode or cathode) of an EL element that includes a light emitting layer containing an organic compound. However, ITO has a high refractive index of approximately 2. Thus, according to the invention, the first electrode is formed of indium tin oxide containing silicon oxide (hereinafter referred to as ITSO). Unlike ITO, ITSO is not crystallized even when baked and remains in the amorphous state. Accordingly, the planarity of ITSO is superior to that of ITO, and the first electrode using ITSO is not short-circuited to the second electrode easily even when a layer containing an organic compound is thin, thus, ITSO is suitable for an electrode of a display element. In addition, when silicon oxide with a refractive index of approximately 1.46 is added, the refractive index of ITSO used as the first electrode can be changed. [0014] Furthermore, a display device that includes ITSO for an electrode and uses for an interlayer insulating film a heat resistant planarized film obtained by an application method generates less heat, leading to improved reliability of the display device. [0015] According to the display device of the invention, light from a light emitting layer is emitted outside of a substrate through stacked layers formed of a material with high light transmittance, whereby increased emission efficiency can be achieved. [0016] According to the invention, a heat resistant planarized film, a first electrode, and an insulating layer (bank) are doped with at least one element selected from the elements belonging to Group 13 or Group 15 in the periodic table, which are impurities of one conductivity type. The doping may be carried out by an ion doping method, a plasma doping method, or an ion implantation method. As the elements belonging to Group 13 or Group 15 in the periodic table, B, Al, Ga, In, Tl, P, As, Sb, and Bi can be employed, and typically phosphorous (P) and boron (B) are employed. At least one element selected from the elements belonging to Group 13 or Group 15 in the periodic table, which are relatively large in atomic diameter, is doped in order to generate distortions and modify or densify the surface (including side walls), thereby preventing moisture and oxygen from entering. In addition, the baking effect of the doping itself allows moisture to be released during the treatment. When the first electrode is also doped with at least one element selected from the elements belonging to Group 13 or Group 15 in the periodic table, physical properties such as resistance can be controlled. [0017] The dosage of at least one element selected from the elements belonging to Group 13 or Group 15 in the periodic table, which is included in the doped region (densified area), may be substantially equal in the heat resistant planarized film, the first electrode and the insulating layer (bank). Specifically, the concentration is preferably in the range of 1.times.10.sup.18 to 5.times.10.sup.21/cm.sup.3, and more preferably in the range of 2.times.10.sup.19 to 2.times.10.sup.21/cm.sup.3. It is to be noted that when a side surface of the insulating layer and a side surface of the planarized film are inclined to have a tapered shape, at least one element (ion species) selected from the elements belonging to Group 13 or Group 15 in the periodic table can be accelerated in an electric field to affect the side surfaces, leading to modification thereof. A taper angle at this time is preferably in the range between 30 and 75.degree.. [0018] According to the invention, in the case of, after forming a contact hole, an element with a conductivity being doped to the periphery of the contact hole, it is possible not only to densify the periphery of the contact hole but also to add the element with a conductivity to a semiconductor layer under the contact hole. Therefore, a high density impurity region can be formed in the semiconductor layer in a self-aligned manner. [0019] At least one element selected from the elements belonging to Group 13 or Group 15 in the periodic table may be doped to each of the heat resistant planarized film, the first electrode, and the insulating layer (bank), or may be doped to one or two of them. Alternatively, it may be doped to the whole surface of them, or may be selectively doped to form a doped region partially. That is, only a side surface of the heat resistant planarized film may be doped with an element and covered with a sealing member, or a contact hole may be partially doped with an element. Needless to say, an element may be doped to the whole surface to make a high density region. [0020] According to the invention, a substance containing an organic material can be used for a heat resistant planarized film and an insulating layer (bank). When such a substance being doped with at least one element selected from the elements belonging to Group 13 or Group 15 in the periodic table, the light transmittance thereof is lowered and the substance is colored. The reflectivity thereof remains low. In the case of the heat resistant planarized film being doped with at least one element selected from the elements belonging to Group 13 or Group 15 in the periodic table, the transmittance and reflectivity thereof are lowered due to the doping and the heat resistant planarized film is colored. In a top emission display device, the colored film can be used as a light shielding film that provides the effect of protecting TFT characteristics and the like. Even in a dual emission or a bottom emission display device, when a passivation film is formed on a heat resistant planarized film, the passivation film is not colored by at least one element selected from the elements belonging to Group 13 or Group 15 in the periodic table, therefore, only a part that exposes the heat resistant planarized film in a contact hole, is colored and densified. Accordingly, even in a dual emission or a bottom emission display device, light can be transmitted and extracted sufficiently. The densified area of a contact hole can prevent moisture from entering. As a result, contamination such as moisture can be prevented from entering through the contact hole, and thus the effect of preventing degradation of a display element is further enhanced. [0021] Furthermore, when doping at least one element selected from the elements belonging to Group 13 or Group 15 in the periodic table, the light transmittance of an insulating layer (bank) is lowered and the insulating layer is colored in black. Accordingly, the light transmittance of the insulating layer (bank) can be controlled so that it is colored in black and used as a black matrix of a display device. According to the invention, an insulating layer (bank) can function as a densified barrier against contamination as well as a black matrix with low light transmittance, low reflectivity, and improved optical properties. As a result, it is possible to provide an inexpensive display device with improved yield and reliability. Continue reading... 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